There are indications of two second messenger systems in lung and certain other tissues. An adrenergic system, mediated via adenyl cyclase and its product cyclic AMP, and a cholinergic system mediated via guanyl cyclase and cyclic GMP. We will study the relative activities of these two enzymes as affected by agonists known to regulate lung, in particular, histamine, serotonin and the prostaglandins. We will complete studies on the intracellular localization of these enzymes. We are interested in determining if the enzyme activities determined in a tissue homogenate are derived from different cellular organelles or a fragment of the same cellular estructure. Studies will be continued on the purification of guanyl cyclase from beef lung. The enzyme needs to be brought to a pure enough state so that if may be characterized.